The present invention relates to a solid-state image sensing device.
The structure of a solid-state image sensing device related to the present invention will be described hereinbelow with reference to FIG. 4, which is a longitudinal cross-sectional view thereof.
Near the surface of a p-type semiconductor substrate 1, an n-type impurity charge storage layer 2 is formed to transfer light allowed to be incident upon the charge storage layer 2 into a signal charge photoelectrically and further to accumulate the transferred signal charge temporarily.
Further, on the surface of the semiconductor substrate 1, an n-type impurity transfer channel 4 is formed in the vicinity of the charge storage layer 2. The signal charge stored in the charge storage layer 2 is given to the transfer channel 4 and further transferred in a direction perpendicular to the paper.
Further, on the surface of the semiconductor substrate 1 and on the charge storage layer 2, a p-type impurity depletion prevention layer 3 is formed for prevention of depletion at the interface of the charge storage layer 2. Extending to near the transfer channel 4, this depletion prevention layer 3 is provided with a function of isolating the transfer channel 4 from the charge storage layer 2, respectively.
A p-type impurity barrier layer 6 is located between the charge storage layer 2 and the transfer channel 4 for prevention of punch through between both from being generated.
A transfer electrode 5 is formed on the transfer channel 4 via an insulating film (not shown) to transfer the signal charge through the transfer channel 4 in response to a pulse signal.
When further microminiaturization in the size of each pixel and further increase in the number of pixels are required for the above-mentioned solid-state image sensing device, the following problem arises: In FIG. 4, a junction length L1 between the barrier layer 6 and the depletion prevention layer 3 must be sufficiently long. In general, this length L1 is about 1 .mu.m. This is because when the junction length L1 is too short, punch through will be generated between the transfer channel 4 and the charge storage layer 2, with the result that the image quality is degraded.
On the other hand, when the impurity concentration of the barrier layer 5 is increased in order to shorten the junction length L1 without generating the punch through between both, there exists a limit. This is because since the barrier layer 6 is formed by thermally diffusing the impurities implanted near the interfaces in the semiconductor substrate 1, the impurities of the transfer channel 4 and of the barrier layer 6 cancel each other in an area 4a of the transfer channel 4 in contact with the barrier layer 6, so the n-type impurity concentration of the transfer channel 4 will be lowered. As a result, there exists a problem in that the transfer capacity of the transfer channel 4 is lowered.